1. Field of the Invention
The present invention relates to a composite loud-speaker apparatus provided with loudspeakers for reproducing audio sound in a full range and a medium/low frequency range and to a method of driving the same, and particularly to a composite loud-speaker apparatus and method of driving the same which is reduced in size and has improved low frequency range.
2. Description of Related Art
FIG. 1 is a drawing showing the configuration of a composite loudspeaker apparatus of the prior art. In the drawing, numeral 1 denotes a full-range loudspeaker for the left (L) channel which reproduces the sound from an audio signal L of the L channel. The full-range reproduction loudspeaker 1 is enclosed in a closed cabinet 2. Numeral 3 denotes a full-range reproduction loudspeaker for the right (R) channel which reproduces the sound from an audio signal R of the R channel. The full-range reproduction loudspeaker 3 is enclosed in a closed cabinet 4.
The composite loudspeaker apparatus of the prior art, is further provided with a synthesis circuit 8 which synthesizes the audio signal L of the L channel and the audio signal R of the R channel, a low frequency range boost up circuit 9 for enhancing the low frequency range of the synthesized audio signals, and a low frequency range reproduction loudspeaker 5 for converting the output signal from the low frequency range boost up circuit 9 into audio sound. The low frequency range reproduction loudspeaker 5 is enclosed in a phase inverting cabinet 6 which has a volume greater than those of the closed cabinets 2 and 4. Inside of the phase inverting cabinet 6 is divided into a small air chamber and a large air chamber. The phase inverting cabinet 6 has a sound port 7 made in a wall of the small air chamber.
Now the operation will be described below. The audio signal L of the L channel is input to the full-range reproduction loudspeaker 1 and converted into audio sound, and the audio signal R of the R channel is input to the full-range reproduction loudspeaker 3 and converted into audio sound. The audio signals L and R of the L channel and the R channel are input to the synthesis circuit 8 where both signals are synthesized, and to the low-frequency range boost up circuit 9 where the signals are enhanced in the low frequency range. The enhanced signal is input to the low frequency range reproduction loudspeaker 5 and is converted into audio sound, The audio sound in the low frequency range radiated from the low frequency range reproduction loud-speaker 5 is enhanced through Helmholtz's resonance between the air in the sound port 7 and the air in the small air chamber, and then radiated from the sound port 7. As a result, the reproduced sound pressure characteristic in the low frequency range is enhanced.
The composite loudspeaker apparatus of the prior art, as constructed as described above, requires three cabinets (2, 4, 6) for the L channel, the R channel and the low frequency range reproduction. Also because increasing the reproduction frequency range for lower frequencies requires increasing the volume of the cabinet 6, greater installation space is needed.